This invention relates to the positioning and control of various types of operating heads that are utilized to move work pieces sequentially through cycles wherein various industrial operations such as die casting, forging, assembly, stamping, welding etc. are performed. More particularly, the invention relates to equipment variously referred to as "robots", "manipulators", "pick and place mechanisms", "extractors", "actuators" etc. and especially to equipment in which an operating head such as prehensile "hand", spray head etc. is carried on an arm capable of several automatically controlled motions to achieve a wide range of travel.
Prior art equipment of the type described often utilizes an operating head, such as tongs or the like, mounted on an arm by a wrist joint that provides tipping motion about a horizontal axis perpendicular to the arm and roll motion about an axis parallel to or extending along the longitudinal center line of the arm. In addition to the tipping motion and roll motion, it is often desirable to have a yaw motion about an axis perpendicular to the plane defined by the tip axis and the roll axis.
Where the operating head is a pair of tongs that operate, for example, in a vertical plane it is desirable to have the means defining the yaw axis (pivot pin, hinge or the like) located as closely as possible to the tongs, preferably between the tip axis and the tongs. This permits the arm to be inserted into a work space and then pivoted laterally about a vertical yaw axis in order to grab the workpiece or the like located at one side or the other of the work space into which the operating head has been inserted. Since the hinge pin is generally vertical, the mechanism that operates the operating head by pivoting it about the yaw axis is not loaded with the weight of the work piece to be carried by the tongs. On the contrary the load or moment is carried by the pivot pin axle or the like, itself rather than by the yaw operating linkage.
In some applications, however, after the operating head, including the tongs and the work piece, is removed from the operating space, the head (and work piece) are rotated about the roll axis. If the head and work piece are rotated such that the tongs are in a horizontal plane perpendicular to the plane in which they initially grasp the work piece, a load is applied in such a way as to create a moment about the yaw axis. This tends to apply stress to the yaw operating mechanism which can be undersirable particularly if the yaw mechanism is fluid operated.
Accordingly, the problem to which the present invention is directed is the elimination of any stress on the yaw operating mechanism after the operating head is returned from a yawed position to a normal, forwardly-extended position and then rolled with the work piece about the roll axis.
The yaw device has particular utility in association with the manipulator shown and described in U.S. Pat. No. 4,417,845 entitled "Programmable Positioning and Operating Mechanism for Industrial Operating Head" granted Nov. 29, 1983. That patent discloses a manipulator specially adapted for use in the die casting industry. In many industrial die casting processes, it is common practice to use a mechanical device to extract castings from the die casting machine. The extractor is synchronized with the operation of the die casting machine and is adapted to extend an arm between the open platens of the die casting machine, grasp the casting, retract the arm and release the casting onto a conveyor belt or place it in a receptacle or quenching bath. In accordance with recent proposals, programmable industrial robots can be utilized as extractors to automatically transport the casting through a more complex set of operations.
Typical automatic devices for performing some or all of the functions desribed above and in which a yaw motion is provided for the operating head are disclosed in the following U.S. Pats.:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 2,998,237 Devol June 13, 1961 3,251,483 Devol May 17, 1967 3,306,442 Devol Feb. 28, 1967 3,306,471 Devol Feb. 28, 1967 3,525,382 Devol Aug. 25, 1970 ______________________________________
The yaw mechanism of the present invention resolves many of the difficulties encountered with prior art devices and affords other features and advantages heretofore not obtainable.